Rake means for use in a grinding mill

ABSTRACT

A pulverizing mill for grinding material having a rotatable grinding ring, and grinding rollers coacting with the grinding ring for pulverizing material therebetween. Rake means are associated with each of the grinding rollers to break up the matted and packed finely ground material clinging to the upper surface of the grinding ring.

United States Patent lnventors Gustav H. Frangquist Mount Prospect; Paul F. Karnstedt, Park Ridge, Ill. Appl. No. 754,362 Filed Aug. 21, 1968 Patented Jan. 19, 1971 Assignee Combustion Engineering, Inc.

Windsor, Conn. a corporation of Delaware RAKE MEANS FOR USE IN A GRINDING MILL 2 Claims, 3 Drawing Figs.

US. Cl 241/61,

241/1 19 Int. Cl B02c 15/00 Field ofSearch 241/58, 60,

61,117,l19,121,167, 52(Cursory), 53(Cursory) [56] References Cited UNITED STATES PATENTS 2,909,330 10/1959 Hardinge 241/58X FOREIGN PATENTS 267,840 3/1927 Great Britain 241/119 Primary Examiner-Donald G. Kelly Attorneys-Carlton F. Bryant, Eldon H. Luther, Robert L. Olson, John F. Carney, Richard H. Berneike, Edward L. Kochey, Jr. and Lawrence P. Kessler ABSTRACT: A pulverizing mill for grinding material having a rotatable grinding ring, and grinding rollers coacting with the grinding ring for pulverizing material therebetween. Rake means are associated with each of the grinding rollers to break up the matted and packed finely ground material clinging to the upper surface of the grinding ring.

PATENTEUJANI 91am 3556;41 sum 1 0P2 FIG.

INVENTOR.

GUSTAV H. FRANGQUIST PAUL E KARNSTEDT W AM ATTORNEY PATENTEU JANI 9197i SHEET 2 0F 2 FIG. .3

INVENTOR.

GUSTAV H. FRANGQUIST PAUL F. KARNSTEDT W of 02W ATTORNEY RAKE MEANS FOR USE IN A GRINDING MILL BACKGROUND OF THE INVENTION In coal and other pulverizing systems, problems are encountered in that the mixture of finely ground material and new feed tends to compact on the upper surface of the grinding ring. The degree of compaction ofpartially ground material depends on a number of factors, such as the moisture content, size of feed and hardness of the material, and the degree of fineness to which it is being pulverized. The capacity and efficiency of a grinding mill is considerably reduced when heavy caking of the ground material is encountered.

SUMMARY OF THE INVENTION The pulverizing mill of our invention provides a rake associated with each of the grinding rollers. The teeth or prongs of the rake have a slight clearance with the upper surface of the grinding ring, so that they will break up any caked material thereon all swing the tines to become gasbome. The teeth are spaced sufficiently from one another so that the coarse material being introduced onto the grinding ring for pulverization can readily pass therebetween.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional side view of a pulverizing bowl ill embodying our invention;

FIG. 2 is an enlarged plan view showing the rake means of the invention; and

FIG. 3 is a side view taken on line 3-3 of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Hooking now to FIG. I of the drawings, numeral denotes a bowl mill for grinding coal s other material therein. Inside the housing is positioned a rotatable bowl or table 12, mounted on shaft 14. Shaft 14 along with the attached bowl I2 is rotated by means of worm wheel 18, which engages worm 16 mounted motor driven shaft 20.

A plurality of grinding elements 0 rollers 22 are rotatably mounted on shafts 24. Three rollers are often used, and they are equidistantly spaced apart. An adjustable spring 26 urges each roller 22 towards the upper surface of the grinding ring 12. A material to be pulverized, such as coal, is introduced into the mill through inlet 28. A gas, usually air, enters through opening 30, and flows through annular space 31 to convey the ground material passing over the lip of the bowl upwardly through the mill interior and into the classifier 34. The gas and material enter the classifier by way of inlets 32, which contain vines for directing the gas tangentially into the classifier. The larger or more coarse particles of material are separated out of the gas stream by centrifugal force, and fall back onto the grinding ring 12 through bottom opening 36 for further grinding. The finer particles of coal are carried along with the gas stream and leave the mill through outlet 38.

Positioned downstream of each roller in the direction of rotation is a rake 50. Each rake contains a rod or bar 52 secured to and supported by the mill ends 56 of the prongs 54 are very slightly spaced for example one-quarter inch, above the upper surface of the grinding ring I2. Since the prongs 54 .are continuously dragging through a at or cake of finely pulverized material clinging to the grinding ring, the tips 56 preferably are made of good wear-resistant material, such as tungsten carbide. The teeth 54 are sufficiently spaced from one another, for example four inches apart, to permit large unpulverized pieces of material to readily pass therebetween.

The operation of the mill will now be described. Material to be pulverized enters the mill through inlet 28. After being pulverized between the upper surface of grinding ring 12 and rollers 22, the pulverized coal particles are thrown outwardly by centrifugal force into annular space 31. Gas flowing through this space picks up the pulverized particles and caries them to the classifier 34. The heavy, oversize particles will be separated out of the stream by centrifu al force in the classifier 34 and fall back onto grinding ring I by way of opening 36. The fine particles will be carried along with the gas stream out of the mill through outlet 38.

As the bowl rotates, the prongs 54 of the rakes drag through any of the partially pulverized material that may have compacted on the upper surface of the grinding ring. This breaks the material up, allowing centrifugal force to move the material into the air stream where it is picked up and conveyed to the classifier. In one installation for grinding phosphate rock, it was found that the addition of the rakes almost doubled the output capacity of the pulverizing mill. At the same time, the power requirement is considerably reduced.

While we have illustrated and described the preferred embodiment of our invention, it is to be understood that such is merely illustrative and not restrictive and that variations and modifications may be made therein without departing from the spirit and scope of the invention. We therefore do not wish to be limited to the precise details set forth but desire to avail ourselves of such changes as fall within the purview of our invention.

We claim:

1. A pulverizing mill comprising a closed casing, a grinding ring mounted within the casing for rotation about a central vertical axis, means for supporting and rotating the grinding ring, means for introducing material to be pulverized onto the grinding ring, there being an annular gas passage between the grinding ring and the enclosing wall of the casing, means for forcing gas upwardly through this annular passage to carry away pulverized particles in suspension rake means associated with each grinding element, each rake means positioned on the downstream side of its respective grinding element in the direction of rotation of the grinding ring, each rake means having a plurality of radially spaced teeth extending downwardly toward the upper surface of the grinding ring, the teeth being positioned such that there is a very slight clearance between them and the upper surface of the grinding ring, so that as the grinding ring rotates, the teeth will break up the compacted partially ground material clinging to the upper surface of the grinding ring.

2. The pulverizing mill set forth in claim 1, wherein the teeth of each rake means are sufficiently spaced apart so as to allow the larger, unpulverized pieces of material to pass therebetween.

222 2? UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3556, 19 Dated January 19, 1971 Inventor(s) Gustav H. Frangquist and Paul F. Karnstedt It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 7, before "partially" insert -th Column 1, line 20, replace "all swing" with -a1lowing--;

Column 1, line 27, replace "ill" with --mi1l--;

Column 1, line 3h, replace "Hooking" with --Looking-;

Column 1, line 35, replace "s" with --or--;

Column 1, line 40, replace "0" with -or--;

Column 1, line 50, replace "vines" with -vanes--;

Column 1, line 58, after "mill" insert --housing. Bolted to bar 52 er a plurality of teeth or prongs 5 The tipsor--;

Column 2, line 2, replace "at" with --mat--;

Column 2, line h, before "good" insert -a-;

Column 2, line 13, replace "caries" with -ca.rries--;

Column 2, line &0, before "means for introducing" insert -a plurality grinding elements mounted to coast with the grindir ring,--;

Column 2, line 4 after "suspension" insert Signed and sealed this 16th day of May 1972.

(SEAL) Attest:

EDWARCMJ'LETCHER, JR. ROBERT GOTTSCHALK Attestlng Officer Comissioner of Patents 

1. A pulverizing mill comprising a closed casing, a grinding ring mounted within the casing for rotation about a central vertical axis, means for supporting and rotating the grinding ring, means for introducing material to be pulverized onto the grinding ring, there being an annular gas passage between the grinding ring and the enclosing wall of the casing, means for forcing gas upwardly through this annular passage to carry away pulverized particles in suspension rake means associated with each grinding element, each rake means positioned on the downstream side of its respective grinding element in the direction of rotation of the grinding ring, each rake means having a plurality of radially spaced teeth extending downwardly toward the upper surface of the grinding ring, the teeth being positioned such that there is a very slight clearance between them and the upper surface of the grinding ring, so that as the grinding ring rotates, the teeth will break up the compacted partially ground material clinging to the upper surface of the grinding ring.
 2. The pulverizing mill set forth in claim 1, wherein the teeth of each rake means are sufficiently spaced apart so as to allow the larger, unpulverized pieces of material to pass therebetween. 